Copy 1 UlMVMSill Ut rit^JNSIljVAlNlA 



The Growth of Field Corn as Affected 
by Iron and Aluminum Salts 



BY 

CHARLES HOMER ARNDT 

M 

[ 



A THESIS 

Presented to the Faculty of the Graduate School in 

Partial Fulfillment of the Requirements for 

The Degree of Doctor of Philosophy 

In Botany 



PRESS OF 

THE NEW ERA PRINTING COMPANY 

LANCASTER, PA. 

1922 



The Growth of Field Corn as Affected 
by Iron and Aluminum Salts 

By CHARLES HOMER ARNDT 

With Plate I and Figures 1 and 6 



CONTENTS 



Introduction • • '* / 

Historical Review 47 

The Present Investigation (Methods and Materials) 50 

Germination 51 

Solution Cultures 52 

Sand Cultures ■ 53 

Experimental Data •• • 54 

I. The Effect of the Composition of the Nutrient Solution upon 

the Availability of Iron in Ferric Phosphate 54 

II. The Effect of Iron Salts in Solution "A" 55 

III. The Toxicity of Aluminum Salts and Acids in Solution "A" . 57 

IV. The Effect of Iron and Aluminum Salts upon Growth in Solu- 

tion "H" 58 

a. Solution Cultures 58 

b. Sand Cultures 59 

Discussion "1 

Summary " y 

Bibliography . ' " 



[Reprinted from the American Journal of Botany, 9: 47-71, February, 1922.] 









THE GROWTH OF FIELD CORN AS AFFECTED BY IRON AND 

ALUMINUM SALTS 

Charles Homer Arndt 
(Received for publication May 17, 1921) 

Introduction 

The investigations of Hoffer and Carr ('20) on corn diseases have shown 
that a brown or brownish-purple discoloration of the lower portion of the 
nodal tissue is frequently associated with evidences of malnutrition and 
of root rot. This discolored area they have designated zone "B." Chem- 
ical analyses showed that a high iron or aluminum content was associated 
with such a discoloration. The injection of iron salts produced a similar 
brownish discoloration, increased the catalase and oxidase activities, and 
reduced the H-ion concentration. Ferrous salts produced these effects 
more readily than did ferric salts. The injection of aluminum salts pro- 
duced no discoloration, but had an effect similar to that of iron salts upon 
the physiological activities. Stalk- and root-rot organisms were usually 
associated with the accumulation of iron and aluminum in zone "B." 
Bordnar ('15) earlier reported a similar correlation between a high aluminum 
content of the sugar beet and its infection by bacterial organisms. His 
analyses showed that a high aluminum content preceded the infection, which 
indicates that an increased aluminum content is in some manner related to 
the decreased resistance to infection. 

The present investigation was undertaken to determine whether toxic 
concentrations of iron and aluminum salts would produce a similar patholog- 
ical condition in corn. With this object in view, a study was made of the 
effect of the composition of the nutrient solution upon the toxicity of 
sulphuric, nitric, and hydrochloric acids and of their corresponding salts 
with iron and aluminum. 

Historical Review 

Some investigators of the toxicity of aluminum sails believed that 
the toxicity is due largely to the acid liberated in the hydrolysis of the 
salts. Abbott, Conner, and Smalley ('13) investigated the effect of alumi- 
num nitrate and nitric acid on field corn. Their results indicated that 
nitric acid is as toxic as the same normality of aluminum nitrate. They 

[The Journal for January (9: 1-46) was issued February 21, 1922.] 

47 



48 AMERICAN JOURNAL OF BOTANY [Vol. 9 

concluded that the toxicity is due to the hydrolysis of the aluminum salts 
with the accompanying liberation of nitric acid. Miyake ('16) has com- 
pared the effect on rice seedlings of the same normality of aluminum chloride 
and hydrochloric acid. The toxicity of these two solutions w r as not greatly 
different. The H-ion concentration produced by the acid was three times 
as great. This indicated that the toxicity must be due to something other 
than the H-ion concentration. A similar conclusion w r as reached by Hart- 
well and Pember ('i8) in their study of the effect of aluminum sulphate on 
barley and rye. The sulphuric acid produced a H-ion concentration four 
times as great as the same normality of aluminum sulphate. The two 
substances were, however, alike toxic to barley. The acid depressed the 
growth of rye similarly to that of barley, but the salt had little effect on 
the rate of growth of rye. This indicated that plants may vary greatly 
in their tolerance of aluminum salts. Duggar ('u) states that the various 
soluble inorganic salts of the same metal are of about equal toxicity. 
Rothert ('06) has shown that this may not be strictly true for aluminum 
salts. Aluminum chloride was found to be much more toxic to corn than 
the sulphate. The toxicity of the salts was also dependent upon the method 
of application. They were most toxic when used alone in distilled water; 
less toxic in Knop's solution ; and least toxic in soil cultures. 

The toxicity of iron salts, particularly of the ferrous salts, w r hen present 
in excess, is well known. Hartwell and Pember ('08) determined the 
effect of ferrous sulphate upon the growth of rye and barley. Katayama 
('06) found that a concentration of ferrous sulphate of less than 0.01 percent 
stimulated the growth of barley. Higher concentrations were toxic. 
Clover, according to Rupprecht ('15), is seriously injured under certain 
conditions by ferrous salts in a concentration above 4 p. p.m. Iron hydrate 
when added to sand cultures is toxic to spinach. Analyses by Czadek 
('04) have shown that iron in this form is easily absorbed by spinach. 

Iron salts, as aluminum salts, are readily hydrolyzed. Thus, they 
produce an increased acidity of the sand or solution cultures. Boiret and 
Paturel ('92) suggested that the toxicity of ferrous sulphate is due to the 
acid radicle. Ferric salts are even more easily hydrolyzed and precipitated 
in nutrient and soil solutions. The generally recognized greater toxicity 
of the ferrous salts, as compared to the ferric salts, indicates that at least 
in the case of the ferrous salts the toxicity is possibly due to something 
other than the acidity. This may be due in part, as has been suggested 
by Awatsu ('14), to an abnormal stimulation of the physiological activities. 
The ferrous salts produce the greater effect on these activities. Maquenne 
and Demousy ('20) found that the addition of small amounts of copper 
sulphate to solutions containing a toxic concentration of ferrous sulphate 
reduced the toxicity. The addition of the copper to like solutions of ferric 
salts did not reduce the toxicity. They believe that the unlike effect is 
due to the catalytic action of the copper which hastens the oxidation of 



Feb., 1922] ARNDT — THE GROWTH OF FIELD CORN 49 

the ferrous salt to the less toxic ferric salt. The addition of calcium salts 
and phosphates to toxic solutions of both salts also lessened the injurious 
effect by aiding the formation of insoluble iron salts. 

It has already been noted that most soluble iron and aluminum salts 
are readily hydrolyzed with an accompanying liberation of the acid radicle. 
Daikuhara ('14), Abbott, Conner, and Smalley ('13), Hartwell and Pember 
('18), and Mirasol ('20) state that all soils which indicate injury to plants 
by aluminum are acid. This acidity is usually reported as the lime require- 
ment of the soil. Recent work by Joffe ('20) indicates that this lime re- 
quirement is closely related to the H-ion concentration. Duggar ('20) has 
shown that the H-ion concentration may be a limiting factor in plant growth 
and that the effect of any particular concentration upon plant growth 
varies with the plant used. Good yields were secured with corn with H-ion 
concentrations varying from a pH of 3.2 to one of 7.1. The optimum H-ion 
concentration depended upon the nutrient solution and possibly to some 
extent upon the environmental conditions. Hoagland ('17) reported that 
a H-ion concentration of 0.3 X io~ 3 is toxic to barley seedlings. These 
facts emphasize the necessity of determining the depression caused by a 
H-ion concentration in the nutrient solution, which lacks the toxic salt, 
equal to that which is produced by the hydrolysis of the iron and aluminum 
salts, if we wish to determine the toxicity of the salt itself. A comparison 
of the depression caused by the salt with that of an equal acidity produced 
by an acid whose anion is of little or no importance as a depressing factor, 
should give some indication of the toxicity of the salt itself. 

Because of the importance of a suitable source of iron in nutrient solu- 
tions, it was necessary to ascertain the proper source of iron and the amount 
necessary to secure the optimum growth of corn. Maze's ('19) experi- 
ments with corn lead him to recommend ferric sulphate rather than ferrous 
sulphate as a source of iron. Shive ('15), Tottingham ('14), and others, 
in the study of the salt requirements of plants, have used ferric phosphate 
as a source of iron. Duggar ('20) has noted that corn grown in Shive 's 
solution becomes chlorotic. The efficiency of ferric and ferrous phosphate 
has been compared by Corson and Bakke ('17). They secured the best 
yield with the ferric salt. Shive and Jones ('21) have found lately that 
the use of ferrous sulphate as a source of iron in wheat cultures gives superior 
growth to that secured in cultures in which ferric phosphate is used. Pre- 
liminary experiments showed that ferric phosphate is not a suitable source 
of iron for corn in solutions of Type 1 as recommended by the Committee 
of the National Research Council on the Salt Requirements of Representa- 
tive Agricultural Plants. Consequently, experiments were made to de- 
termine the form of iron necessary to assure a sufficient supply to prevent 
a lack of it from limiting the growth of the plants. 



50 american journal of botany [vol. 9 

The Present Investigation 

Solution cultures were used in the main part of this experimental work. 
These results were checked with sand cultures to determine to what extent 
the solution cultures might indicate the toxicity of these salts in the soil. 
In all cases the weight of the plants grown in the unmodified solution was 
taken as the control. The effect of the acid or salt is indicated as the per- 
centage of the weight of the plants grown in solutions containing them, 
as compared with the control culture. The weight in the control was 
taken as ioo percent. For the tops the green weight was used as a criterion 
of the relative growth, as this probably gives the best indication of the 
condition of the plants. Comparisons of the green and dry weights gave 
similar relative weights. As a criterion of the root development, the dry 
weight was used. The roots were placed in weighed test tubes and dried at 
ioo° C. for several days. 

The H-ion concentration for the solutions was determined by means 
of the Lubs and Clark (Clark, '20) series of indicators, using the buffer 
mixtures recommended by them. These were carefully prepared from re- 
crystallized salts. Standards were kept in Pyrex test tubes of 10 cc. 
capacity, the solutions to be tested were placed in similar test tubes, and 
the same concentration of the indicator was added to them. The H-ion 
concentration of the sand cultures at the time of the renewal of the solutions 
was determined by adding distilled water to bring the sand to 60 percent 
of its water-holding capacity; 50 cc. of the solution was drawn off by suction 
through a hose previously rinsed with distilled water; the new solution 
was then added, and the remaining 450 cc. was withdrawn. The pH value 
is reported for the 50 cc. and for the total 500 cc. drawn off. All solutions 
were clear. Consequently, turbidity did not interfere with the determina- 
tions. The pH values given to show the effect of the growth of the plants 
upon the reaction of the solution were determined just previously to the 
time of harvesting the plants. This was usually at the end of a warm, 
sunny period favorable for growth, as these conditions seemed to have an 
important effect on the results. 

The seed corn used in these experiments was Reid's Yellow Dent, a 
variety of yellow dent (or, according to Sturtevant ('94), Zea mays var. 
indentata), which was furnished by Dr. G. N. Hoffer. It gave practically 
100 percent germination. Very few grains showed any infection by parasitic 
organisms. The salts used were Raker "analyzed" chemicals. The 
ferric phosphate was prepared as recommended by the Committee of the 
National Research Council on Salt Requirements of Representative Agri- 
cultural Plants. All stock solutions of the salts and acids were made up 
as TV/ 10 solutions. These were made up fresh at least twice a week, except 
the ferrous sulphate which was made up immediately before it was used. 
The distilled water was prepared with a Barnstead still and was stored in 
glass containers. 



Feb., 1922] ARNDT — THE GROWTH OF FIELD CORN 51 

In the solution cultures, pint Mason jars and colorless cylindrical 
museum jars of 900 cc. capacity were used. These were treated with clean- 
ing fluid for several hours before each experiment. The jars were com- 
pletely covered with opaque black paper. A loose shell of stiff light-brown 
cardboard was placed over this. Flower pots were used for the sand 
cultures. These were thoroughly impregnated with heated paraffin and 
then well coated on the inside with a thin layer of the same. The sand 
was procured from the Whitall Tatum Company. It is the brand known 
as "Juniata." It was prepared as recommended by the Committee on the 
Salt Requirements of Representative Agricultural Plants. It had a water- 
holding capacity of 32 percent. It was kept at 60 percent of its water- 
holding capacity throughout the experiment by the method recommended 
by the above-named Committee. 

The relative transpiration of the plants grown in the various solutions 
was determined from the amount of water added daily to replace the water 
which had been lost. The relative transpiration here reported is based 
on the loss for a certain period immediately preceding the time when the 
plants were harvested. During this period the evaporating power of the 
atmosphere was determined by standardized spherical white and black 
atmometer cups. To keep the conditions of light and temperature as 
nearly uniform as possible for all cultures, as no rotating tables were avail- 
able, the plants were shifted daily in a systematic manner so that each 
plant occupied the same position for about the same period during the 
experiment. 

Each solution culture contained four plants. Five plants were grown 
in each pot in the sand cultures. In most cases the cultures were run in 
duplicate series, so that the relative growth is based on the total weight of 
eight or ten plants. The weights reported in the tables are based on the 
mean weight of one plant. 

Germination 

The seed used was carefully selected for uniformity of size and shape. 
The seed was soaked for 15 minutes in tap water, drained, and allowed to 
stand at room temperature for two hours. It was next treated for 15 
minutes with a 5 percent calcium hypochlorite solution (5 g. per 100 cc). 
This was removed by washing the seed several times with boiled tap water. 
It was finally soaked for 12 hours in a shallow covered dish in just sufficient 
boiled water to cover the seed. After soaking, the seeds were distributed 
on filter paper in germinating dishes and covered with a layer of filter 
paper. The dish was placed in the greenhouse, covered with glass, and 
flooded once a day with water. When the radicles were one centimeter 
long, the seeds were removed to a paraffined germination net made of coarse 
netting. This was stretched over an inverted twenty-liter bell jar, and 
filled with a solution of one tenth the concentration of the solution R2S3 



52 AMERICAN JOURNAL OF BOTANY [Vol. 9 

of the Type 1 solutions recommended by the Committee on the Salt Re- 
quirements of Representative Agricultural Plants. In addition, 2 g. of 
calcium carbonate was added to each jar. Tap water was used instead of 
distilled water. Consequently, the exact composition of this solution is 
not known, but as it gave excellent results, it was probably as good as any 
solution which can be used until we have some definite information con- 
cerning the effect of various solutions on the germination of corn. The 
seedlings were left on the net until the shoots were about 6 cm. long. This 
required from 6 to 9 days. Ten times as many seeds were soaked as were 
finally used. This number was reduced by one half at the time the seedlings 
were transferred to the net. At the time the seedlings were transferred to 
the solutions a second selection of the best seedlings was made. For the 
solution cultures these were wrapped loosely with cotton above the seed 
and placed in one-half-inch holes in paraffined corks. When they were to be 
grown in sand, the seed was placed just below the surface. 

Solution Cultures 

(a) Solution "H." The solution which Hartwell and Pember ('18) 
found satisfactory for studying the effect of aluminum sulphate on barley 
and rye, was found to be well adapted for the growth of corn. It was 
modified slightly to secure a better growth of corn. Its composition, as 
used, is as follows: 

CaH 4 (P0 4 ) 2 0.00005 M MgS0 4 0.0008 M 

Ca(NO,) 2 0015 M A1 2 (S0 4 ) 3 000003 M 

NH4NO3 001 M M11SO4 00001 M 

KG 0008 M ZnS0 4 000005 M 



Total 0.004168 M 

To this was added 7 mg. of FeP0 4 per liter. For convenience, this 
solution will be referred to as solution "H." Preliminary experiments 
indicated that Hartwell's solution gave the best results when aluminum, 
zinc, and manganese were added. The work of Maze ('15) on the salt 
requirements of corn suggested this modification. The phosphate con- 
centration of the solution used is about twice that recommended by Hart- 
well and Pember. There was no sign of precipitation when aluminum 
salts were added and the solution was allowed to stand a week. Again, 
all solutions were changed every other day, or at one half the interval used 
by Hartwell and Pember. The ferrous-sulphate solutions were changed 
every day to prevent, as far as convenient, the change from the ferrous to 
the ferric condition. It was impossible to prevent precipitation when the 
ferric salts were used. Consequently, the results may not truly represent 
the relative toxicity of the ferrous and the ferric salts. 

(b) Solution "A." A number of preliminary experiments demonstrated 
that with solutions of Type 1 as recommended by the Committee on the 



Feb., 1922] ARNDT — THE GROWTH OF FIELD CORN 53 

Salt Requirements of Representative Agricultural Plants, a solution of one 
half the molecular concentration of R 2 S 3 was well within the range necessary 
for the optimum growth of corn. A solution was used whose partial 
volume-molecular proportions were as follows: KH 2 P0 4 , 0.0024 M\ Ca- 
(N0 3 ) 2) 0.0036 M; MgS0 4 , 0.0035 M. This solution probably had an 
osmotic pressure close to 0.5 atmosphere. 

In this solution it was impossible to prevent precipitation when the 
various salts were added. Consequently, the results of the experiments 
in which this solution was used are not strictly comparable with those in 
which solution "H" was used. They are comparable when considered in 
relation to the effect of the composition of the nutrient solution upon the 
tolerance of acidity by corn. Because of this precipitation, a renewal of 
the solutions at small intervals would have had little effect on the amount of 
the salt in the solution. To economize time, the ferrous sulphate solutions 
of 0.001 iVand higher were changed twice a week; the others were changed 
once a week. 

Sand Cultures 

Solution "H" was used in all sand cultures. The method of McCall 
('16) as modified by Johnson ('20) was used for changing the solution. 
The cultures containing ferrous sulphate were renewed every day; the 
others, every third day. The sand did not contain sufficient iron for the 
optimum growth of corn. Ferric phosphate was added to the solution as 
in the solution cultures. The ferric phosphate was added to the ferrous- 
sulphate cultures every third day, as most of the phosphate probably was 
held in the sand and was not withdrawn when the solutions were renewed. 

After 2000 g. of sand was placed in each pot, it was thoroughly washed 
a second time by drawing 3 liters of distilled water through it. The sand 
used for the acid cultures was treated for 48 hours with strong sulphuric 
acid and then thoroughly washed until the water withdrawn was neutral. 
These sand cultures were not covered with a wax seal. This was thought 
desirable in order to simulate soil conditions as far as possible. A wax 
seal would have reduced the aeration and induced conditions in the soil 
which would undoubtedly have increased the toxicity of the ferrous salts. 
In order to secure some idea of the relative amount of water lost through 
evaporation and transpiration, a pot without plants was placed in the 
series and treated as the others. The amount lost through transpiration 
was calculated by deducting the loss from this pot from the total loss of 
the other cultures. The error introduced by this method of determining the 
transpiration should be small, as the loss through evaporation was relatively 
small in comparison to the total water loss. 

The writer wishes to express to Dr. J. W. Harshberger his sincere appre- 
ciation of the interest and assistance which made possible the experiments, 
and to acknowledge his indebtedness to Dr. G. N. Hoffer of the Office of 



54 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9 



Cereal Investigations of the United States Department of Agriculture for 
the suggestion of the problem and for much valuable information. Dr. 
Alice M. Russell has added greatly to the interest of the investigation by 
her mycological study of the discolored nodes. To Dr. R. H. True and to 
other members of the Botanical Department of the University of Pennsyl- 
vania, the writer is greatly indebted for generous help and criticisms. 



Table i. The Effect of the Composition of the Nutrient Solution upon the Availability of 

Iron in Ferric Phosphate 





Mg. FeP04 
per 
Liter 


Total Weight 


Relative Weight 


Solution 


Tops 


Roots 


Tops 


Roots 


"H" 

"A" 

"A" 

"A" 


7 

3-5 
14 
35 


82.6 gm. 
34-4 
43-9 
59-84 " 


3.84 gm. 
2.24 " 

2-3 
3-68 " 


IOO% 

42 s 

53% 
72% 


J 00% 

58% 

59% 
97% 







Experimental Data 

I. The Effect of the Composition of the Nutrient Solution Upon the Avail- 
ability of Iron in Ferric Phosphate 

Four cultures were set up in duplicate as shown in table 1. The plants 
were grown in the 800-cc. jars during the period from February 7 to March 
5, 1921. The "H" solutions were changed twice a week; the others every 



Pri 












Tops 














\\ ' 


roots — 
Initial pH 










ptfafi 


' grow 


//1 — 




- — — 








\ \ ' 

\ \ 


/ 

\ / 




-— — 


\\ 








\ \ 


\ / 






\\ 












If \ 




\ 
















*■*•-«, 



I I I I I I I I I 1 1 -J 

7 3.5 /4 3S 0.0000s o.oooi 0.0002 00005 0.001 00000s o 000s 0001 0002/V 
mqm. perZ. ft P0 4 ' F e S0 4 ' ^ ("°3 ) 3 

Fig. 1 (left). Relative growth of roots and tops with FeP0 4 in solution "A" (3.5, 
14, 35) and "H" (7). 

Fig. 2 (right). Relative growth in solution "A" with FeSO.) and Fe(N0 3 )s. Also 
H-ion concentration before and after growth. 



Feb., 1922] 



ARNDT — THE GROWTH OF FIELD CORN 



55 



week. All the plants in solution "A" were unquestionably chlorotic, 
which fact indicated that they did not secure sufficient iron. The plants 
grown in solution " H " were of a normal color. Other experiments showed 
that an increase of iron in this solution did not increase the yield. An 
increase in the amount of ferric phosphate in solution "A" did increase the 
yield. The color of the plants, however, indicated that the iron was not 
available in sufficient quantities. Plate IV and also figure 1 show clearly 
the difference of growth in the various concentrations. 



II. The Effect of Iron Salts in Solution "A" 

Two preliminary experiments, in which ferrous sulphate was used as a 
source of iron, were made in the fall of 1920. This was a poor period for 
growth because of the great amount of cloudy weather. The results are 
of interest in comparison with those of the experiment performed under 
more favorable conditions during March, 1921. In this experiment, the 
plants were grown for 25 days in 800-cc. jars. The first two experiments 
will be referred to in table 2 as series 1 and 2 respectively; the latter as 
series 3. The relative transpiration is reported for the last week of growth 
for series 3. During this period the average daily loss from the white and 
the black atmometer was 11.4 cc. and 13.6 cc. respectively. 

Table 2. The Effect of Iron Salts upon the Relative Yields of Tops and Roots and upon 
Transpiration in Solution "H" — Also the Initial pH and the pll After Growth 

















pH 












Yield of 


Trans- 








Nor- 




Yield of Tops 


Roots 


piration 


Ini- 
tial 


After Growth 


Salt 
















mality 


Ser. 1 


2 


3 


3 


3 


1 


2 


3 


O.OO 




35% 










4-7 


5 




FeS0 4 .... 


O.OOOO5 
.OOOI 






74% 
75 


88% 
92 


81% 

75 


« 






6.7 
6.6 


" 


.0002 




66% 


88 


IOO 


84 


" 




5-b 






.0005 


100 

(2.6 gm.) 


100 

(4.21 gm.) 


100 
(24.7 gm.) 


IOO 
(0.48 gm.) 


100 

(790CC.) 




5-5 






" 


.OOI 


68 


66 


54 


67 


52 




5 


5-2 


b-2 


" 


.002 


62 


63 










4-3 


4.1 




" 


.004 


47 












4 






" 


.008 


21 










" 


3-5 






Fe(N0 3 ) 3 . 


.00005 






3? 


38 


38 


" 






6.8 


* * 


.0005 






68 


73 


70 


3-9 






0./ 
6.6 


" 


.OOI 






7i 


74 


7i 


3-5 








.002 






5i 


63 


53 


3-2 






4.0 



All plants grown in the solutions containing ferric nitrate were chlorotic. 
This fact, and the low yields associated with it, indicated that ferric nitrate 
was much inferior to ferrous sulphate as a source of iron in solution "A." 
In all cases, the best yield was secured with 0.0005 N ferrous sulphate. 
The above-noted results for series 3 are shown graphically in figure 2. A 
comparison of figures 1 and 2 shows that the lack of iron does not usually 



56 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9 



depress root development as much as it does that of the tops. It is in- 
teresting to note the poor root development in 0.0005 N ferric nitrate. 
There is little difference in the relative growth with either salt in 0.001 N 
and 0.002 N. It is singular that ferric nitrate should begin to depress 
growth before it supplies sufficient iron for normal growth. 




Qon H SO HH0 3 MCI ^% *"$ #Cl M&M/Uto,), ^»o, A K N0 3 h *IC1 3 

" i_ 0^^^ ' ' O.OOI N. ' Q.0OO4»4O0Q8»O.0Ot6N O0QO8M 



Fig. 3. Relative growth and the H-ion concentration upon the addition of acids and 
aluminum salts to solution "A." The H-ion concentration is given for the initial solution 
and at the end of the first and last weeks of growth. 

Table 3. The Eject of Acids and Aluminum Salts in Solution "A " 





Nor- 
mality 






Rel. 
Transpir- 
ation 


pH 


Sol. "A" 
plus 


Rel. Weight 


Ini- 
tial 


After Growth 


Tops Roots 


i?t wk. 


4th wk. 


0.00 


O.OOO5 
.OOI 
.0005 
.OOI 
.0005 
.OOI 
.0004 
.0008 
.OOl6 
.OO08 
.OOO8 


IOO% 
(io.l gm.) 
95 
77 
87 
45 
90 
46 
98 
87 
65 
91 
93 


100% 

(0.24 gm.) 
105 
73 
77 
38 
100 
38 
93 
81 

69 
89 
98 


100% 

(560 CC.) 

89 

75 

89 

53 

84 

44 
89 
83 
82 

85 
88 

1 


4.8 

3-6 
3-3 
3-4 
3-2 
3-5 
3-2 
3-9 
3-7 
3-4 
3-9 
3-8 


6 

5-4 

4 
4.8 

3-6 

5-2 

3-6 

6 

5-2 

5 

5-2 

5-6 


6.4 


H 2 S0 4 

HNO3 

HCl 

A1 2 (S0 4 ) 3 .... 

Al(NO,), .".'!! 
A1C1 3 


6 
6 
6.2 

5-2 
6.2 
4.8 
6.2 
6.2 

5-2 

6.4 

6.2 



Feb., 1922] 



ARNDT THE GROWTH OF FIELD CORN 



57 



III. The Effect of Aluminum Salts and Acids Upon Growth in Solution "A" 

The object of this series of experiments was to determine the relative 
toxicity of hydrochloric, nitric, and sulphuric acids and their corresponding 
aluminum salts. The solution was modified by the addition of the acids 
and the salts as shown in table 3. As previously stated, the aluminum 
salts were precipitated in this solution, and the concentration added does 
not represent the amount remaining in solution. The results, consequently, 
do not represent the real relation between the toxicity of the acid and that of 
the salts. The plants were grown for 30 days during the month of April in 
a shaded greenhouse. Pint Mason jars containing 400 cc. of the culture solu- 
tions were used. The results are shown graphically in figure 3. The 
weather was very favorable during the first portion of the period. There 
was practically no sunshine during the last week. This fact, undoubtedly, 
accounts for the small change in the pH value for the last week of growth. 

Table 4. The Effect of Acids and Iron and Aluminum Salts upon Growth in Solution "H" 



Sol. "H' 

plus 



PH 



Nor- 
mality 



Yield of Tops 



Ser. 1 



Yield of 
Roots 



Transpir- 
ation 



Ini- 
tial 



After 
Growth 



Control. . 
H2SO4... 

HNO3... 

UCA.. '.'.'. 

FeSO„. . . 
Fe 2 (S0 4 ) s 
Fe(N0 3 ) 3 
FeCl 8 . . . 
AI,(S6 4 ')', 

AI(N0 3 ) 3 
A1C1 3 .... 



.0004 
.0006 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 
.0001 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 
.0002 
.0004 
.0006 



100% 

(17.5 gm.) 
97 
7i 
88 
90 
82 
68 

97 
82 
69 
72 
62 

41 
100 

72 
75 
97 
69 

52 
95 
86 

67 
9i 

84 

73 
64 

63 
53 
50 



100% 100% 100% 
(20.2 gm.) (0.58 gm.) ' (745 cc.) 



67 

76 
62 



63 
7i 

52 



67 

73 

62 
64 



7i 
65 

69 

55 

7i 
53 
66 

54 



66 
61 

65 

57 



74 
69 

68 
51 

84 
49 
60 
50 



52 
67 

54 
59 



63 


61 


56 


51 


5i 


54 


88 


88 


84 


74 


73 


66 


62 


59 


52 


57 


67 


53 


66 


67 


63 


57 


50 


52 


53 


48 


45 


73 


74 


66 


64 


62 


52 


64 


60 


49 



4-9 

3-7 

3-5 

3-2 

3-7 

3-4 

3-2 

3-7 

3-5 

3-2 

4.6 

4.6 

4.2 

4 

3-7 

3-5 

4 

3-7 

3-5 

4 

3-6 

3-5 
4.2 
4.1 
3-9 
3-8 
4.2 
4.2 

4 

4.2 
4.1 
3-9 



4-9 



6.2 



6.2 
6 

6 
5-6 

6.2 

5-4 
4.4 

3-8 



4-7 

4-7 

4.6 
4-7 

4-7 
3-3 
5-8 
4-8 

4.2 

4 
4.6 

3-7 
4.2 

4 
3-9 

3-5 



58 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9 



The pH value at the end of the first week is also given. The water loss by 
transpiration is given for the entire growth period. The average daily- 
loss from the white and black atmometers was 5.83 cc. and 6.49 cc., re- 
spectively. 



IV. The Effect of Iron and Aluminum Salts Upon Growth in Solution "H" 

(a) Solution Cultures. As solution "H" has been previously described, 
only a brief account of the experiment and the environmental conditions 
will be given here. The pint jars and 450 cc. of the culture solutions were 
used in all cases. Series 1 was run for 37 days during January and February. 
Conditions for growth at the beginning of the experiment were not very 

'100 





















1 
Tops 










■ 








?H 




















Initial pH 






















/ 


>S7 after 1 


yrvcoi 


ft 








7 


***« 






































6 






















1 

/ 


^ 
















\ 






/• 


\ 












/ 

i 






s 






, X 


I 


' 




















\ 






,.--' 


\ 




■pr" 




\ 












k - 


3 











































C H-5 H-N H'CfttS Ftps F-/Y F-C A-5 A-N /? -C H-S H-ff H-C ftifS F-ff F-C 

O. OOO 6 /*■ 



AS A-N A-C 



0.000 2. rv 



Fig. 4. Relative weight of tops and H-ion concentration before and after growth in 
solution "H" as they were affected by the addition of acids and salts in 0.0002 iVand 0.0006 
N concentration. In this and the following figures, the following notation is used: C, 
control; H, F, and A denote the cations H, Fe, and Al. The anions are indicated thus: 
5 = S0 4 ; N = N0 3 ; C = CI. Ferrous and ferric sulphate are distinguished by plus signs; 
F^ + S — ferrous sulphate, F+++ S = ferric sulphate. 

favorable. Conditions were very favorable for growth during the 37-day 
period in which series 2 was grown. The plants grew rapidly and seemed 
to be in excellent condition until several days before the end of the experi- 
ment, when the leaves of some of the plants were unable to open because of 
the formation of a mucilage-like substance. This was most noticeable in 
the solutions containing aluminum. This pathological condition was 
associated with a number of bright sunny days during which it was im- 
possible to keep the greenhouse temperature below 32 C. It never ex- 
ceeded 35 C. The relative transpiration is given for series 2 and is based 
upon the transpiration for the last week of growth. During this period the 
average daily loss from the white and the black atmometers was 11.4 cc. 
and 13.6 cc, respectively. 



Feb., 1922] 



ARNDT — THE GROWTH OF FIELD CORN 



59 



_(b) Sand Cultures. The plants in the sand cultures were grown for 
40 days in April and May. The modifications of solution "H" and the 




Fig. 5. Relative growth of tops and roots, transpiration, and the H ion concentration 
before and after growth in solution " H " upon the addition of 0.0004 N ac id ar >d salts. For 
notation see figure 4. 

results are given in table 5. The transpiration is reported for the last 16 
days of growth. The total average loss by evaporation from the pots with- 
out plants, which was deducted from the total loss of the others to determine 
the amount lost by transpiration, was 405 cc. During the period of growth 
the average daily loss from the white and black atmometers was 7.83 cc. 
and 8.5 cc. respectively. The small difference between these values is 
due to the fact that the plants were grown in a well shaded greenhouse and 
to the large proportion of cloudy weather during the first part of the ex- 
periment. On sunny days the temperature ranged from 30 C. to 35 C. 
This was probably too high for the optimum growth of corn. The pH 
values are given for the first 50 cc. and for the total 500 cc. drawn off at the 
end of the second week, and also at the time of the last renewal for which 
the pH value of the last 50 cc. is also given. The change in the pH values 
of the initial solutions by plant growth was much greater in the sand cultures 
than in the solution cultures, as is well shown in figure 6. The depression 
of growth of the tops is also on an average less, and particularly so in case 



6o 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9 



Table 5. The Effect of Acids and Iron and Aluminum Salts upon Growth in Sand Cultures 



Sol: "H" 
Plus 



Nor- 
mality 



Weight 
of Tops 



Root 
Score 



Control 



HNOs 
HC1. . 
FeS0 4 



H2SO4 O.OOI 

.002 

.001 

.001 

.0002 

.0004 

.0006 

.0004 

.0004 

.0004 

.0002 

.0004 

.0006 

.0002 

.0004 

.0006 

.0002 
.0004 
.0006 



Fe 2 (S0 4 ) 3 . 
Fe(NO s )a. 
FeCl 3 .... 
A1 ? (S0 4 )3. 



A1(N0,), 
A1C1«... 



100% 
(12.8 gm 

9i" 

59 
101 

89 
102 
88 
49 
79 
80 
66 
69 
66 
57 
73 
54 
54 
80 

63 
56 



21 

16 

8 

14 
11 

23 

2 

o 
10 
8 
6 
4 
3 

6 
5 

9 
1 



pH 



Transpi- 
ration 



Ini- 
tial- 



End 2d wk- 



End last wk. 



50 
cc. 



IOO% 
(1410 cc.) 
100 
52 

98 

86 
99 
79 
60 

75 
69 
61 
70 
69 
58 
74 
64 
58 
76 
67 



4.9 6.2 



I rst 500 Last 
50 cc.| cc. 50 cc. 



3 

2.8 

3 

3 

4.6 
4.6 

4-2 

3-7 
3-7 
3-7 
4.1 

3-9 
3-9 

4-2 

4-2 

4 

4-2 

4-1 

4 



5-4 

3-4 

5 

5-4 

5-8 

5-6 

3-8 

5-8 

5-6 

6 

6 

5-8 

6 
6 

5-8 
6.2 



6.2 

3-8 

3 

3-8 

3-8 

5-6 

5-6 

3-6 

5-8 

5-8 

5-8 

6 

5-8 

6 
6 

6 
6.2 



6.4 

5-6 

3-4 
6 

5-6 

4.8 

4.4 

3-4 

5-8 

5-2 

5-6 

6.2 

5-8 

4.1 

6.2 

5-4 

4 

6 

5-4 
4 



3-8 

3 

4 

3-6 

4.6 

4.2 

3-4 

5-2 
5 
5 
6 

5-2 

4 

6 

4.8 

5 

5-8 

4.8 

4 



3-6 

3 

3-6 

3-6 

4.6 

4.2 

3-6 

5 

4.8 

4.8 

5-8 

4.8 

5-8 
4.8 

5-4 
4.8 



of the peculiar behavior of ferrous sulphate at 0.0002 N and 0.0004 N. This 
difference is probably accounted for by the better aeration of the sand 
cultures. It is still more unusual to have the lower concentration give a 
slightly higher yield than the control, and 0.0004 N a higher yield than the 
same concentration of the ferric salts. This is probably to be explained by 
the fact that the ferrous solutions were renewed every day; the others every 
3 days. The addition of sand to the culture solution changed greatly the 
toxicity of the acids. The average depression in the sand cultures for 
0.001 N acid was 6 percent, and in the solution cultures for 0.0004 N it 
was 21 percent. 

The aluminum salts produced approximately the same depression in 
both types of cultures. The corresponding average depressions in the 
sand and solution cultures for 0.0002 N are 26 percent and 28 percent, and 
for 0.0004 N, 39 percent and 40 percent, respectively. The extensive 
researches of Shive ('20) have indicated that this similarity in effect in 
sand and solution cultures is to be expected when the solutions are changed 
at frequent intervals, and that such factors as chemical action and pre- 
cipitation must not be considered. 

The inhibiting effect upon root development of the acids and of the iron 
and aluminum salts was much less in the sand than in the solution cultures. 
A 0.0006 N concentration of ferrous sulphate in the sand cultures in- 

1 These results are taken from a series run previous to the time the other cultures were 
grown. 



Feb., 1922] 



ARNDT — • THE GROWTH OF FIELD CORN 



61 



hibited their development relatively less than 0.0002 N in the solution 
cultures, 0.001 N H 2 S0 4 less than 0.0006 N; and 0.0004 N of the aluminum 
salts much less than 0.0002 N. In the solution cultures the dry weight was 
used as a criterion of relative root growth. The results, for reasons to be 




0.OOO.2.7V. O.OOOfN O.00O6K O.OOIX 0.00m 

Fig. 6. Relative growth in sand and solution cultures and the effect of plant growth 
upon the H-ion concentration. For notation see figure 4. 

discussed later, were not satisfactory. In this experiment the roots were 
washed free of sand and then compared by the method devised by Free 
('15). A comparison can readily be made by reference to the numbers 
reported. The highest number indicates the best root development. 

Discussion 

It is plainly evident from the experiments described in the preceding 
pages that the effect of any particular salt upon plant growth depends 
largely upon the composition of the solution in which the plants are grown. 
One of the best examples is the difference in the availability of the iron in 
ferric phosphate in solutions "A" and "H." Something in solution "A" 
prevents the plant from absorbing the iron. This is not due to any in- 
herent property of the ferric phosphate. At the time series 2 of experiment 
4 was run, plants were grown in a modified solution "H." The calcium 
phosphate was replaced by an equivalent molecular weight of ferric phos- 
phate. The growth of the tops in these cultures relative to the control 
was 95 percent; of the roots, 68 percent, and the transpiration was 96 per- 
cent. The plants were as well developed as those of the controls. The 
lower nodes of these plants did not show any discolored nodes, such as were 
found when the plants were grown in the solution with this concentration 



62 AMERICAN JOURNAL OF BOTANY [Vol. 9 

of the other iron salts. This behavior of ferric phosphate was very interest- 
ing when it formed as a precipitate when ferric nitrate was added directly 
to solution "A." A 0.001 N concentration did not produce plants of a 
normal green color. A 0.002 N concentration was decidedly toxic. It is 
singular that growth should be depressed by the addition of an iron salt, 
before sufficient iron is available for the growth of the plant. When the 
efficiency of ferric nitrate as a source of iron is compared with that of 
ferrous sulphate, the result is striking. At 0.0005 N, the yield in the latter 
is 68 percent of that in the former; while at 0.001 A T , the ferrous salt be- 
comes very toxic and the ferric salt gives the better yield. This greater 
physiological activity of the ferrous salt may be correlated with its greater 
influence on catalytic activities. Other factors, however, may be con- 
cerned. The ferrous salt is less readily precipitated than the ferric. There 
may also be a difference in the solubility of the two phosphates which may 
be influenced by the concentration of phosphorus and calcium in the solu- 
tion. Any attempt at an explanation of this difference can be only specu- 
lative until more data are available. 

The concentration of ferrous sulphate necessary to give the maximum 
yield with corn in solution "A" is probably close to 0.0005 N. This is 
approximately 14 mg. per liter. The iron requirements of corn are evi- 
dently very different from those of wheat and probably also from those of 
rice as determined by Shive and Jones ('21) and Gile and Carrero ('20). 
The findings of Corson and Bakke ('17) apparently are not applicable to 
corn. It is somewhat difficult to interpret Maze's recommendation of 
a ferric rather than a ferrous salt. He used a concentration of 50 mg. of 
ferrous sulphate per liter, an amount which would have been extremely 
toxic in solution "H." Maze ('13) noted that everything depends on the 
relative proportion of all elements. This is well illustrated by the behavior 
of ferrous sulphate in solutions "H" and "A." A concentration of it in 
solution "H," two fifths of that required for optimum growth in solution 
"A," reduced the yield 25 percent to 30 percent. A doubling of this con- 
centration in solution " H " reduced the yield almost 50 percent. The three 
ferric salts are about alike toxic, and their effect upon growth in solution 
"H," when compared to ferrous sulphate, is practically of the same order 
as the relative efficiency of ferric nitrate and ferrous sulphate in promoting 
growth in solution "A." At a 0.0002 N concentration they are practically 
without effect upon the yield ; and at 0.0004 N, they gave about a 15 percent 
better yield than the ferrous salt. 

The toxicity of aluminum salts at the higher concentrations does not 
seem to be a function of the concentration. The average depressions are: 
0.0001 A 7 10 percent, 0.0002 A 7 28 percent, 0.0004 ^4° percent, 0.0006 A 42 
percent in the solution cultures, and 0.0002 N 26 percent, 0.0004 N 39 
percent in the sand cultures. There is an increase in toxicity of aluminum 
salts, as measured by yield of tops, with increasing concentration; but it is 



Feb., 1922] ARNDT — THE GROWTH OF FIELD CORN 63 

not at all proportional to the increase in concentration. The effect on the 
development of the roots is more nearly related to the concentration. This 
difference in root development is much greater than is actually indicated 
by the small differences in the relative root yields. The development of 
the small secondary roots is inhibited at the higher concentrations; but 
coinciding with the stunting of the secondary roots there is a thickening 
of the main roots and an increased formation of prop roots, which increases 
the weight of the root system. Because of this fact, the dry weight is a 
poor criterion of the root development and of the number of feeding roots. 
In the solution cultures, the roots were barely able to penetrate a solution 
of 0.0006 N, no secondary roots formed, and the root tips were frequently 
swollen and recurved. Nevertheless, the roots were able to absorb sufficient 
material to produce a stunted growth. The poor development of the roots 
in the higher concentration probably accounts to some extent for the 
tendency of chlorosis to be associated with aluminum injury. It is likely 
that the capacity of aluminum salts to antagonize the action of iron salts, 
as has been noted by Stoklasa ('18&), may be the most important factor. 

The effect of aluminum salts on root development described above 
is similar to that noted by Rothert ('06) in his study of the effect of aluminum 
chloride and sulphate upon the growth of Zea mays. He states that the 
shoots suffer the least and the secondary roots the most. A 1 percent 
solution was necessary to depress growth in Knop's solution, which is 
many times the concentration necessary to depress growth in solution 
"H." Hartwell and Pember ('18) secured a 44 percent depression of the 
growth of barley with 0.0008 N aluminum sulphate in solution "H." It 
is very likely that this concentration would not produce a much greater 
depression with corn. 

Some interesting suggestions as to the possible cause for this peculiar 
action of aluminum «alts may be found in the studies of Stoklasa ('18a, b), 
Berthelot and Andre ('95), and Meurer ('08). The latter has shown that 
the amount of aluminum absorbed by slices of beet or carrot roots from a 
solution of one of its salts is independent of the concentration of the salt 
in the solution. Tissue killed by chloroform absorbs the aluminum as 
readily as living tissue. He concludes that aluminum forms some chemical 
compound with the pectic bodies of the middle lamella. The relatively 
lesser toxicity of aluminum salts at increased concentrations has led 
Stoklasa ('18&) to conclude that aluminum combines with the cell wall to 
form colloidal salts. This action renders the cell less permeable. The 
researches of Sziics ('12) demonstrated that it also acts on the protoplasm 
and causes it to set. The singular thickening of the main roots of the 
plants grown in the solution cultures is probably due to some unique action 
of the aluminum upon the tissues of the root. Berthelot and Andre grew 
plants in pot cultures to which aluminum salts were added. In all the 
plants grown in their cultures, aluminum oxide formed a much larger 



64 AMERICAN JOURNAL OF BOTANY [Vol. 9 

percentage of the ash of the roots than of the tops. They concluded that 
aluminum after absorption is fixed and thus rendered immobile. Stoklasa 
('18a) has shown that the amount of aluminum in the roots of mesophytic 
plants is determined largely by the amount of soil moisture. An increase 
in the soil moisture increased the percentage of aluminum in the roots, 
but not in the tops in which the percentage was always low. These facts 
probably explain the lessened depression of root growth by the aluminum 
salts in the sand cultures. Rothert's analyses of the corn plants which he 
grew in the cultures containing aluminum showed a large percentage of 
aluminum in the ash of the roots and only a trace in the tops. Hoffer and 
Carr ('20) have shown that most of the aluminum which is carried to the 
stem accumulates in the nodal area. Microchemical tests made with plants 
grown in the present experiment confirm this finding. 

In the present investigation no evidence has been found to confirm 
Rothert's statement that aluminum chloride is more toxic than aluminum 
sulphate. There is some indication of a slightly greater toxicity of the 
aluminum nitrate. 

The H-ion concentrations of solutions "A" and "H" are slightly below 
those which Duggar ('20) has given as the optimum for corn. The slight 
depression of growth caused by 0.0002 N concentration of H 2 S0 4 in solution 
"H," by 0.0005 N in solution "A," and by 0.001 N in the sand cultures, 
indicates that an initial acidity above pH 3.7 in solution "H," above pH 
3.6 in solution "A," and above pH 3.6 in the sand cultures had little effect 
upon the growth of field corn. When the initial concentration of the acid 
in solution "H" is increased to 0.0004 N (pH 3.5), there is a distinct de- 
pression which is greater than that caused by 0.001 N (pH 3) in the sand 
cultures. A 0.0006 N concentration of nitric, hydrochloric, or sulphuric 
acid is decidedly toxic in the solution cultures. The three acids produced 
a similar depression of the relative weight of tops and roots. The roots 
were much better developed in the sulphuric acid solutions, when compared 
with the effects of the other acids, than is indicated by the relative weights. 
A similar difference was noted in the solutions containing the three ferric 
salts. This feature is clearly shown in Plate IV, figure C. The difference 
in development is in harmony with the favorable effect of sulphates on the 
root development of certain plants which has been noted by Tottingham 
and Hart ('15). In solution "A," as shown in figure 3, the sulphuric acid 
gave a better yield of the tops than did the other acids. This is most 
marked with a concentration of 0.001 N. The relative yields reported in 
this paper, indicating the effects of the various concentrations of the acids 
in solution "H" on corn, are very similar to those given for wheat, barley, 
and oats by Hartwell and Pember ('07). 

It will be noted from the tables and figures that the solutions in general 
tended to become less acid with the growth of the plants. A similar tend- 
ency has been noted by Duggar ('20), Salter and Mcllvaine ('20), and 



Feb., 1922] ARNDT — THE GROWTH OF FIELD CORN 65 

Hoagland ('19). The acid solutions were more readily shifted toward 
neutrality than the solutions containing the iron and aluminum salts. 
There seems to be a tendency for the sulphuric acid solutions to be shifted 
most readily, particularly in solution "A." The effect of the acid radicle 
of the aluminum salts in determining the shifting of the reaction is shown 
by a comparison of the initial H-ion concentration and the concentration 
after growth. This is well shown by the various graphs. The sulphate 
solutions, with the exception of those containing ferrous sulphate, are 
unique in that in all cases the H-ion concentration was shifted toward 
neutrality. The reverse was true of the solution cultures containing ferrous 
sulphate even at the low concentration of 0.0002 TV. , All solutions contain- 
ing nitrates become less acid except 0.0004 N aluminum nitrate. The 
chlorides showed a strong tendency to increase the initial H-ion concentra- 
tion. This tendency was shown by all concentrations of aluminum chloride 
in solution " H," and also by 0.0006 N ferric chloride. In the sand cultures 
the 0.0006 N ferrous sulphate solution was the only one which showed 
after plant growth a H-ion concentration higher than the initial concentra- 
tion of the solution. 

The results of Salter and Mcllvaine show that a H-ion concentration less 
than that necessary to depress growth in solution "H" may produce a 
distinct depression in other nutrient solutions. They found that a reaction 
of pH 4. 1 1 was much less favorable to corn than a reaction of pH 5.16, in 
their strongly buffered solutions. The great changes in the reaction of 
solutions "A" and "H" produced by the growth of corn indicate that 
possibly the initial concentration of the solution is not as important a 
factor in plant growth as is the buffer action of the solution which determines 
the ease with which the plant can shift the reaction. It is very likely that 
the toxicity of the acids in solutions "A" and "H" could have been in- 
creased either by using larger amounts of the solutions, or by renewing 
them more frequently. A survey of the tables will show that the shifting 
of the reaction is roughly proportional to the size of the plant. Thus, the 
pH values given in table 3 and figure 3 show that the change in the reaction 
is greater at the end of the fourth than at the end of the first week; and in 
table 4 it appears that the series (ser. 2) which gave the greatest total 
growth also produced the greatest change in reaction. 

In solutions containing ferrous sulphate, growth shifted the H-ion con- 
centration in the opposite direction. The change was almost negligible 
at the beginning; but as the plants became larger, the H-ion concentration 
was increased. A solution with a similar concentration of the salt was 
kept in the greenhouse in a flask for three days without a change equal to 
pH 0.2. It seems fairly evident that the' plant in some manner accelerates 
the hydrolysis and the precipitation of the salt and is the main agency 
which produces the change in acidity. The ferric salts are immediately 
precipitated, giving a high initial acidity to the solution. The ferrous salt 



66 AMERICAN JOURNAL OF BOTANY [Vol. 9 

is less readily precipitated, but when conditions are such as to favor its 
precipitation a similar acidity is produced. 

A comparison of the relative yields in solution "H," as shown in figures 
4, 5, and 6, of the acids and the aluminum salts, points to the cation of the 
salt rather than the H-ion concentration produced by the hydrolysis of the 
salts as the toxic factor. The reverse is true in solution '.'A" (fig. 3). The 
results in solution "H" indicate that corn is affected by soluble aluminum 
salts similarly to rice (Miyake, '16) and barley (Hartwell and Pember, 
'18; Conner, '21). A closer relation seems to exist between t e ability of 
the plant to shift the reaction toward neutrality and the relative toxicity 
of the acid and the salt, than exists between the initial H-ion concentration 
and the toxicity of the salt. This inability of the plant to change the 
reaction may be a secondary feature, for, as has been previously pointed 
out, this change is related to the amount of plant growth and it may be 
merely a measure of the toxicity of the solution rather than the cause of 
the toxicity. These results are not in harmony with the conclusions of 
Abbott, Conner, and Smalley ('13). These authors based their conclusions 
largely upon the root development of seven-day-old seedlings. Plate IV, 
figure B, which shows the relative development in 0.0004 N acid and in 
the same normality of the corresponding aluminum salts, indicates that 
there is a distinct difference between the toxicity of the acid and that of 
the salts as measured by root development when a longer period of growth 
is used. These results agree with those of Miyake. He based his con- 
clusions on the relative elongation of the shoots and states that there is 
little difference in the toxicity of the same strengths of the acid and of the 
salt. His results on root elongation show that the root growth in the acid 
was twice as great as in the corresponding salt solution. The relative 
toxicity of the acid and the salt in solution " H " depends somewhat on the 
concentration used. Except in the case of sulphuric acid, there is little 
difference in the toxicity of the acid and of the corresponding salt in a 
0.0006 N concentration ; while at 0.0002 N, the acid has practically no effect 
upon growth and the salt produces a considerable reduction of growth. 
A comparison of the relative effects of the acid and of the salt, as shown 
by the results given for the sand cultures in table 5 and in figure 6, is even 
more favorable to the acid. These results are also more dependable when 
considered in relation to the H-ion concentration, as the buffer action of 
the sand kept the concentration more constant; although it is possible 
that the concentration reported does not represent the acidity of the solu- 
tion in contact with the roots. In these cultures a 0.002 N concentration 
of sulphuric acid in the culture was necessary to produce the same depression 
as 0.0006 N aluminum sulphate. The difference in H-ion concentration 
is still greater. In the acid cultures it was approximately four times as 
great, as marked by the difference between pH 3.4 and pH 4.1. This 
indicates that the theory advanced by Abbott, Conner, and Smalley, which 



Feb., 1922] ARNDT THE GROWTH OF FIELD CORN 67 

states that the toxicity of aluminum nitrate toward field corn is largely due 
to the acidity produced by the hydrolysis of the salt, is no longer tenable. 
It has been previously noted that all soils which show aluminum injury 
are acid. A comparison of the pH values reported at the end of the second 
and at the last renewal (5th week) in the sand cultures shows an increase 
in acidity of the cultures by the continued addition of aluminum salts, 
which fact supports the belief that the hydrolysis of aluminum salts may 
be an important factor in the production of soil acidity through the reac- 
tions noted by Noyes ('19). 

Hartwell and Pember ('08, p. 293), after their investigation of the 
effect of the same normality of sulphuric acid and ferrous sulphate on 
barley and rye, conclude that the injury caused by the salt is largely due 
to the liberation of the acid radicle in hydrolysis. A comparison of the rela- 
tive growth which they report for 0.0004 N ferrous sulphate and the growths 
given here in table 4 shows that this is not the case with corn in solution 
"H." A 0.0002 N ferrous-sulphate concentration depressed the growth 
almost 30 percent, but it did not produce an acidity greater than pH 4.4. 
Since the H-ion concentration of the solution used by Hartwell and Pember 
is not stated, it is somewhat difficult to compare their results with those of 
the present experiment. A still greater difference will be noted in the sand 
cultures where a 0.0006 N concentration of ferrous sulphate produced a 
10 percent greater depression than 0.002 N sulphuric acid. The H-ion 
concentration of both cultures is the same. The score given in table 5 
to indicate the relative root development is very favorable to the acid 
solution. The cultures in solution "A" show most clearly that the toxicity 
of ferrous sulphate is in no way related to an increase in acidity. The 
0.001 N ferrous sulphate culture never showed a H-ion concentration below 
that of the initial solution, but it did produce a 35 percent to 45 percent 
reduction of growth. 

The toxic effects of the ferric salts in the solution cultures were more 
nearly related to the H-ion concentration than was the case with either the 
ferrous or the aluminum salts. This is because they are immediately 
precipitated. Thus, they produce a high initial H-ion concentration. In 
the sand cultures the 0.001 A 7 acids gave a far better yield than a 0.0004 N 
concentration of the iron salts. A comparison of the acids and the ferric 
salts in these cultures is probably not permissible because the rapid pre- 
cipitation of these salts probably caused a much higher concentration of 
iron in the sand cultures than is indicated by the original solution. If such 
was the case, the increased relative injury as compared with the solution 
cultures must have been due to the precipitated, but probably slightly 
soluble, ferric phosphate and hydroxide. 

The results given in tables 2 and 3 and plotted in figures 2 and 3 seem to 
indicate that in solution "A" the toxicity of iron and aluminum salts is 
largely due to the acidity produced when the salts are precipitated. The 



JO AMERICAN JOURNAL OF BOTANY [Vol. 9 

than the same normality of the other two acids. This difference was even 
more favorable to the sulphuric acid when the root development was com- 
pared. The nitrates and chlorides of aluminum and iron also depressed 
root growth more than the sulphates. 

With solutions "A" and "H," an initial H-ion concentration less than 
pH 3.7 had little effect upon the rate of growth. In most cases the plant 
tended to shift the reaction toward neutrality. On the contrary, when 
ferrous sulphate and certain concentrations of the chlorides were added to 
the cultures, plant growth increased the initial H-ion concentration of the 
solution. The reaction was most readily shifted toward neutrality when 
the acidity was due largely to sulphuric acid and least readily when due to 
hydrochloric acid. The amount of shifting of the reaction was approxi- 
mately the inverse of the toxicity of the salt or of the acid; i.e., the change 
in reaction was proportional to the size and the activity of the plant. 

The toxicity of ferrous sulphate showed no relation to the initial H-ion 
concentration. A 0.0002 N concentration depressed growth 27 percent in 
solution "H." The ferrous sulphate was approximately twice as toxic as 
the same normality of the ferric salts. The latter were more readily pre- 
cipitated, and their depressing effect was closely related to the H-ion con- 
centration produced by their hydrolysis or precipitation. 

In solution "A" the aluminum salts were readily precipitated, and their 
toxicity was evidently due largely to the H-ion concentration thus pro- 
duced. In solution "H" the toxicity was due to the aluminum ion. A 
0.0002 TV concentration produced about the same depression as the same 
normality of ferrous sulphate. The development of the secondary roots 
was inhibited by a 0.0006 N concentration. The nitrate seemed to be some- 
what more toxic than the other aluminum salts and showed a greater 
tendency to produce chlorosis. 

Sand cultures greatly increased the concentration of acids necessary 
to produce the same effect when compared to their effect in the solution 
cultures. The same concentration of the salts produced about the same 
depression of the relative weights of the tops in both types of cultures. 
The use of the sand medium lowered the toxicity of the salts to the roots 
proportionally more than it increased the yield of the tops. 

The composition of the nutrient solution had a greater influence in 
determining the toxicity of the salts than the medium in which the plants 
were grown. 

Iron salts when present in injurious concentrations produced a reddish- 
brown discoloration of the lower portion of the nodal area. Aluminum 
salts collected in the same position but produceed no discoloration. 
Botanical Laboratories, 

University of Pennsylvania 

BIBLIOGRAPHY 
Abbott, J. B., Conner, S. B., and Smalley, H. R. ('13). Ind. (Purdue Univ.) Agr. Exp. Sta. 

Bull. 170. 1913. 
Awatsu, H. ('14). Arch. Inf. Pharm. Therap. 23: 325-352. 1914. 



American Journal of Botany. 



Volume IX, Plate IV. 




M^h-MOt-JkmMOi-teir yci ml 




XCl-MO* ALSO, Con- 1 .n^04) J ./ifA/t 3 ) J .F t CI 3 



Arndt: Growth of Field Corn 



Feb., 1922] ARNDT — THE GROWTH OF FIELD CORN 71 

Berthelot and Andre, G. ('95). Compt. Rend. Acad. Sri. Paris 120: 288-290. 1895. 

Boiret, H., and Paturel, G. (92). Ann. Agron. 18: 417-440. 1892. 

Bordnar, J. ('15). Biochem. Zeitschr. 69: 245-256. 1915. 

Clark, W. M. ('20). The determination of hydrogen ions. Baltimore, 1920. 

Conner, S. D. ('21). Jour. Amer. Soc. Agron. 13: 113-124. 1921. 

Corson, G. E., and Bakke, A. L. ('17). Proc. Iowa Acad. Sci. 24: 477-482. 1917. 

Czadek, O. von ('04). Zeitschr. Landw. Versch. Oesterr. 7: 65-67.' 1904. Abstr. in 

Exp. Sta. Record 15: 964. 1904. 
Daikuhara, G. ('14). Bull. Imp. Cent. Agr. Exp. Sta. Japan 2: 1-40. 1914. 
Duggar, B. M. ('11). Plant physiology. New York, 1911. 

■ ('20). Ann. Mo. Bot. Gard. 7: 1-49. 1920. 

Free, E. E. ('15). Plant World 18: 249-256. 1915. 

Gile, P. L., and Carrero, J. O. ('20). Jour. Agr. Res. 20: 32-62. 1920. 

Hartwell, B. L., and Pember, F. R. ('07). Ann. Rept. R. I. Agr. Exp. Sta. 20: 358-380. 

1907. 

('08). Ann. Rept. R. I. Agr. Exp. Sta. 21: 286-294. 1908. 

■ ('18). Soil Sci. 6: 259-277. 1918. 

Hoagland, D. R. ('17). Soil Sci. 3: 547-560. 1917. 

('19). Jour. Agr. Res. 18: 73-117. 1919. 

Hoffer, G. N., and Carr, R. H. ('20). Phytopath. 10: 56, 57. 1920. 

Joffe, J. S. ('20). Soil Sci. 9: 261-266. 1920. 

Johnson, E. S. ('20). Soil Sci. 10: 389-409. 1920. 

Katayama, T. ('06). Bull. Coll. Agr. Tokyo 7: 91-93. 1906. 

McCall, A. G. ('16). Soil Sci. 2: 207-253. 1916. 

Maquenne, L., and Demousy, E. ('20). Compt. Rend. Acad. Sci. Paris 117: 218-222. 1920. 

Maze, P. ('13). Ann. Inst. Pasteur 27: 651-681. 1913. 

('15). Compt. Rend. Acad. Sci. Paris 160: 21 1-214. 1915. 

C19). Ann. Inst. Pasteur 33: 139-173. 1919. 

Meurer, R. ('08). Jahrb. Wiss. Bot. 46: 502-567. 1908. 

Mirasol, J. ('20). Soil Sci. 10: 153-218. 1920. 

Miyake, J. ('16). Jour. Biol. Chem. 25: 23-26. 1916. 

Moore, B. ('14). Proc. Roy. Soc. London, B, 87: 556-570. 1914. 

Noyes, H. A. ('19). Jour. Ind. Eng. Chem. 11: 1040-1042. 1919. 

Rothert, W. ('06). Bot. Zeit. 64: 43-52. 1906. 

Rupprecht, R. W. ('15). Mass. Agr. Exp. Sta. Bull. 161. 1915. 

Salter, R. M., and Mcllvaine, T. C. ('20). Jour. Agr. Res. 19: 73~95- I9 2 °- 

Shive, J. W. ('15). Physiol. Res. 1: 357-378. 1915. 

■ ('20). Jour. Agr. Res. 18: 327-397. 1920. 

— — and Jones, L. H. ('21). Soil Sci. 11: 93-100. 1921. 
Stoklasa, J., et al. ('18 a). Biochem. Zeitschr. 88: 292-322. 1918. 

('18 Z>). Biochem. Zeitschr. 91: 137-232. 1918. 

Sturtevant, E. L. ('94). Bull. Torrey Bot. Club 21: 319-343- l8 94- 
Sziics, J. ('12). Jahrb. Wiss. Bot. 52: 269-332. 1912. 
Tottingham, W. E. ('14). Physiol. Res. 1: 133-245. 1914. 

and Hart, E. B. ('15). Jour. Agr. Res. 5: 233-250. 1915. 

True, R. H. ('21). Jour. Amer. Soc. Agron. 13: 91-107. 1921. 

EXPLANATION OF PLATE IV 

Fig. A. Relative growth in solutions "A" and "H" when FeP0 4 was supplied as a 
source of iron. Numbers 1, 2, and 3 are in solution "A," with 3.5, 14, and 35 mg. FeP0 4 
per 1., respectively. Number 4 is solution "H " with 7 mg. FeP0 4 per 1. 

Fig. B. Effect of 0.0004 N acids and their aluminum salts in solution "H." 
Fig. C. Effect of 0.0004 N acids and their ferric salts upon root development in 
solution "H." 



LIBRARY OF CONGRESS 



lUlllllVllllllllflll 

002 681 964 7 



